The present invention relates to an evaporation apparatus for forming a metal membrane on a film.
FIG. 7 shows an example of a conventional evaporation apparatus. The apparatus comprises a film 1 on which a membrane is formed by evaporation; a material 2 to be vapor-deposited on the film 1; a vacuum evaporation source 3 consisting of resistance heating, high frequency induction heating, or electron beams for melting and evaporating the material 2; a grounded can 4 rotating in opposition to the vacuum evaporation source 3 and containing cooling liquid which is circulating therein to cool the surface of the film 1 on which the material 2 is being vapor-deposited; a supply roller 5 for supplying the film 1 to the can 4; an ungrounded winding roller 6 for winding the film 1, on which the material 2 has been vapor-deposited, the surface of which contacts the film 1 and is covered with an insulating tape or an insulating coating material such as polytetrafluoroethylene; an ungrounded free roller 7a, for assisting the winding or travel of the film 1, the surface of which contacts the film 1 and is covered with an insulating tape or an insulating coating material such as polytetrafluoroethylene; an ungrounded free roller 7b for assisting the winding or travel of the film 1 and conductive with the surface of the film 1 on which the material 2 has been vapor-deposited; a vacuum chamber 8; a vacuum pump for evacuating the interior of the vacuum chamber 8; a DC power source 10 for applying, through the free roller 7b, a DC voltage to the film 1 on which the material 2 has been vapor-deposited.
The operation of the apparatus with the above construction is described below with reference to FIG. 7.
The interior of the vacuum chamber 8 is evacuated to a vacuum degree of approximately 5.times.10.sup.-5 Torr by the vacuum pump 9 such as a rotary pump, oil diffusion pump, or a cryopump. Then, the supply roller 5, the can 4, and the winding roller 6 are rotated. The film 1 travels in the order of the supply roller 5, the free roller 7a, the can 4, the free rollers 7b and 7a and is wound around the winding roller 6. Thereafter, the material 2 is melted and evaporated by vacuum evaporation source 3 consisting of resistance heating, high frequency induction heating or electron beams. Evaporated particles splash and are deposited on the surface of the film 1 being fed along the surface of the can 4 opposed to the film 1. Thus, a membrane is formed on the surface of the film 1. At this time, the DC power source 10 applies a positive voltage or a negative voltage to the material-deposited film 1 through the free roller 7b so as to generate potential difference between the film 1 and the can 4. As a result, the film 1 which has been brought into contact with the can 4 is cooled by the can 4 containing cooling liquid which is circulating therein. The film 1 then travels to the free rollers 7b and 7a and is wound around the winding roller 6.
According to the above construction, the evaporated material-deposited film is cooled in close contact with the can in early stage of evaporating process due to the difference between the voltage of the can and that of the film. Therefore, the film can be prevented from being thermally extended, contracted or melted by the condensation heat of particles which have been vapor-deposited on the film and the radiant heat emitted by the evaporation source. But when the evaporating operation is performed for a long time, the film is thermally deformed because of the temperature rise of the can. In order to prevent the thermal transformation of the film, it is necessary to bring the film into close contact with the can.